The invention relates to a device for conveying layers comprising a multitude of individual objects, in particular glasses, cans, etc., preferably for loading and unloading pallets.
In this context, conveying is understood to mean both the lifting and the transporting as well as the setting down of layers comprising a multitude of individual objects.
The invention concerns the layered palletizing and depalletizing of individual objects. For this purpose, use is customarily made of a palletizer with a suction head, the objects being held at their top side by means of suction air. The suction head for a palletizer of this type is customarily constructed in such a way that a plurality of suction holes is connected to a common suction chamber with a source of negative pressure. The source of negative pressure is designed in such a way that, with a relatively small negative pressure, no great amount of air is conveyed. At the same time, a resilient layer of padding is frequently arranged on the underside, which layer of padding is placed on the top side of the objects to be lifted, whilst being squeezed to a certain extent, and thereby ensures that the negative pressure is indeed effective on the top side of the objects.
Of course, the suction head must have at least as many suction holes as individual objects are provided within one layer. However, since the individual objects within one layer are frequently not aligned absolutely precisely or the relative position of the individual objects within the layer does not correspond precisely to the arrangement of the suction holes in the suction head, a relatively large number of small suction holes must be provided for proper holding of all the individual objects of one layer and, to be precise, with such spacing that the top side of an individual object is always in the region of at least one suction hole. On the other hand, this results, particularly in the case of round individual objects, in the fact that individual suction holes are not allocated to an individual object and therefore ambient air is taken in via these "vacant" suction holes. If this is the case with several suction holes, the negative pressure breaks down and thus proper holding of the individual objects of a layer is no longer possible.
To avoid this disadvantage, it has already been proposed to reduce the flow cross section of those suction holes which, in individual cases, are not allocated to an individual object in order in this manner to take in as little air from the surroundings as possible via these "vacant" suction holes. For this purpose, valves are provided in the region of all the suction holes, which valves partially close the suction holes under corresponding pressure conditions in order in this manner to reduce their cross section. However, due to the provision of a valve in the region of each suction hole, this construction is very complex. Besides, this constructionally complex design is, relatively speaking, very susceptible to faults, in particular in respect of the risk of impairing the action of the valve due to particles of dirt contained in the air taken in.